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MTU 1010 is an early maturing and high-yielding mega rice variety widely grown in an area of 3 Mha. It is characterised by limited grain number and panicle branching. To improve the grain number in MTU 1010, an IRRI breeding line, IR121055-2-10-5 was utilized as donor to transfer yield-enhancing genes Gn1a and OsSPL14 (associated with increased grain number and better panicle branching, respectively) into MTU1010 by Marker-Assisted Backcross Breeding (MABB). At each backcross generation, foreground selection was carried out with Gn1a and OsSPL14- specific molecular markers, whilst background selection was done with a set of SSR markers polymorphic between the IR121055-2-10-5 and MTU1010. With the use of a gene-specific marker, homozygous BC2F2 plants carrying the yield-enhancing gene were identified and advanced through pedigree-method of selection till BC2F6 and best performing ten lines were selected and evaluated in replicated station trials for yield contributing traits, where grain number and brancing per panicle exhibited high significant and positive correlation with single plant yield. Three promising lines namely RP6353-5-8-13-24, RP6353-26-13-39-5 and RP6353-32-12-8-16 with higher grain number and yield than MTU1010 were identified and nominated for evaluation in Initial Varietal Trial-Aerobic (IVT-Aerobic) of All India Crop Improvement Programme on Rice (AICRP), of which RP6353-26-13-39-5 (IET28674), was promoted for further testing. [ABSTRACT FROM AUTHOR]

Varalu is an early maturing rice variety widely grown in the rainfed ecosystem preferred for its grain type and cooking quality. However, the yield of Varalu is substantially low since it is being affected by reproductive drought stress along with the blast disease. The genetic improvement of Varalu was done by introgressing a major yield QTL, qDTY 12.1 , along with two major blast resistance genes i.e. Pi54 and Pi1 through marker-assisted backcross breeding. Both traits were transferred till BC 2 generation and intercrossing was followed to pyramid the two traits. Stringent foreground selection was carried out using linked markers as well as peak markers (RM28099, RM28130, RM511 and RM28163) for the targeted QTL (qDTY 12.1), RM206 for Pi54 and RM224 for Pi1. Extensive background selection was done using genome-wide SSR markers. Six best lines (MSM-36, MSM-49, MSM-53, MSM-57, MSM-60 and MSM-63) having qDTY 12.1 and two blast resistance genes in homozygous condition with recurrent parent genome of 95.0%-96.5% having minimal linkage drag of about 0.1 to 0.7 Mb were identified. These lines showed yield advantage under drought stress as well as irrigated conditions. MSM-36 showed better performance in the national coordinated trials conducted across India, which indicated that improved lines of Varalu expected to replace Varalu and may have an important role in sustaining rice production. The present study demonstrated the successful marker-assisted pyramiding strategy for introgression of genes/QTLs conferring biotic stress resistance and yield under abiotic stress in rice. [ABSTRACT FROM AUTHOR]

Swarna-Sub1, a ruling submergence tolerant variety of rice, showed a significant decrease in the yield in major blast disease prone areas, which is caused by fungus Magnaporthe oryzae (Pyricularia oryzae). To overcome this problem, three major blast resistance genes viz., Pi1, Pi2, and Pi54 were pyramided through marker-assisted backcross breeding using donors, Swarna-LT (having Pi1 + Pi54) and Swarna-A51 (having Pi2). Foreground selection was carried out using molecular markers tightly linked to three blast resistance genes and also submergence tolerance for retaining the Sub1 gene in the recurrent parent. Based on disease resistance and agro-morphological performance of backcross-derived lines, we selected the best 25 plants of two- and three-gene pyramided BC3F2 homozygous lines with a maximum of ~ 93.5% recurrent parent genome and were further advanced to the BC3F5 generation. The stringent recurrent parent genome recovery analysis using SSR markers limited the linkage drag from a minimum of 0.2 Mb to a maximum of 2 Mb in all three-gene pyramided lines. The two and three blast resistance genes pyramided lines, i.e., SS30-24-82, SS30-24-73, and SS30-24-46, displayed a high level of blast resistance and submergence tolerance. The successful use of marker-assisted backcrossing strategy coupled with phenotypic selection helped in the development of Swarna-Sub1 lines having multiple blast resistance genes with superior agro-morphological and grain quality traits, which could serve as valuable genetic stocks in the rice breeding program. [ABSTRACT FROM AUTHOR]